What is it? Help!

Right over my left ovary it is pretty sore and is swollen. I talked to my step mom and she said it could be a cyst. I haven't had a cyst in a while because I was put on birth control to prevent them so I don't remember exactly what they feel like. Also I'm not sure exactly when I'll start my period but I start taking the sugar pills Sunday. Normally I have a 28 day cycle but last month it was 35 days currently I'm on cycle day 20. What could it be? The pain feels like a bad bruise but there's not bruise there. Edit : someone please comment i just want to know